CN111357136B

CN111357136B - Sulfur-carbon composite material and lithium-sulfur battery comprising same

Info

Publication number: CN111357136B
Application number: CN201880069108.2A
Authority: CN
Inventors: 赵恩京; 高童郁; 孙权男; 梁斗景
Original assignee: LG Energy Solution Ltd
Current assignee: LG Energy Solution Ltd
Priority date: 2017-11-03
Filing date: 2018-10-05
Publication date: 2022-09-06
Anticipated expiration: 2038-10-05
Also published as: US11611067B2; EP3675248A4; WO2019088475A1; EP3675248A1; KR102229450B1; JP2020532843A; US20200280052A1; CN111357136A; JP6908778B2; KR20190050424A; EP3675248B1

Abstract

The present invention relates to a sulfur-carbon composite material and a lithium sulfur battery comprising the same, and more particularly, to a sulfur-carbon composite material comprising a porous carbon material, a polymer having electrolyte supporting ability, and sulfur, wherein the porous carbon material coated with the polymer having electrolyte supporting ability is mixed with sulfur. The present invention can improve the reactivity of sulfur and an electrolyte by introducing a coating layer comprising a polymer having an electrolyte supporting ability onto the surface of the porous carbon material, thereby improving the performance and life characteristics of a lithium-sulfur battery.

Description

Sulfur-carbon composite material and lithium-sulfur battery comprising same

Technical Field

This application claims the benefit of korean patent application No. 10-2017-0145812, filed on 3.11.2017 with the korean intellectual property office, the disclosure of which is incorporated herein by reference in its entirety.

The present invention relates to a sulfur-carbon composite material and a lithium-sulfur battery comprising the same.

Background

As electronic devices and communication devices have recently become rapidly smaller, lighter, and more complex and the necessity of electric vehicles has been highly highlighted in consideration of environmental issues, there has been an increasing demand for improving the performance and life of secondary batteries used as energy sources for these products. As a secondary battery satisfying such a demand, a lithium sulfur battery using a sulfur compound as a positive electrode active material has been receiving attention.

A lithium sulfur battery is a secondary battery using a sulfur compound having a sulfur-sulfur bond as a positive electrode active material and using lithium metal, a carbon-based material having intercalation/deintercalation of lithium ions, or silicon, tin, or the like alloyed with lithium as a negative electrode active material.

In a lithium-sulfur battery, when discharged, a reduction reaction occurs by accepting electrons from sulfur in a positive electrode, and an oxidation reaction occurs by ionizing lithium in a negative electrode. In particular, the sulfur is cyclic S before discharge ₈ And storing and generating electric energy using a redox reaction in which the oxidation number of sulfur decreases as the sulfur-sulfur bond is broken during the reduction reaction (discharge), and increases as the sulfur-sulfur bond is formed again during the oxidation reaction (charge).

In particular, the lithium sulfur battery has a theoretical discharge capacity of 1675mAh/g and a theoretical energy density of 2600Wh/kg, which is as high as about 5 times that of the lithium ion battery (about 570Wh/kg) currently under study, and thus is a battery capable of achieving high capacity, high energy density, and long life. In addition, sulfur, which is a main material of the positive electrode active material, has the following advantages: lithium sulfur batteries have been widely studied due to their low atomic weight, easy availability due to abundant resources, low price, no toxicity, and environmental friendliness, and are advantageous for use as energy sources for medium to large-sized devices such as electric vehicles, as well as portable electronic devices.

Sulfur used as a positive active material in a lithium-sulfur battery has a value of 5X 10 ^-30 Electrical conductivity of S/cm and is non-conductiveSince the electric property is not a conductor, there is a problem that electrons generated by an electrochemical reaction are difficult to transfer. Thus, in use, the sulfur has been complexed with a conductive material, such as carbon, that is capable of providing sites for electrochemical reaction.

Meanwhile, lithium sulfur batteries have not been commercialized because initial capacity and cycle life are rapidly reduced as the cycle proceeds in practical driving, and thus sufficient performance cannot be ensured. This is due to the fact that sulfur as a positive electrode active material undergoes volume expansion due to a reduction reaction, or is lost due to lithium polysulfide as an intermediate product being dissolved into an electrolyte during the reduction reaction and no longer participating in charge and discharge reactions of the battery. Therefore, in order to improve the stability and electrochemical reactivity of the sulfur-carbon composite material, various techniques have been proposed.

As an example, korean patent application publication No. 2016-0046775 discloses that by providing a positive electrode coating layer formed of an amphiphilic polymer on a portion of the surface of a positive electrode active site comprising a sulfur-carbon composite material, it is possible to improve the cycle characteristics of a battery by promoting lithium ion migration and suppressing the elution of lithium polysulfide.

Further, korean patent application publication No. 2016-.

The sulfur-carbon composite materials proposed in these patents have improved the problem of sulfur loss to some extent by coating, however, the effect is still insufficient in terms of stability and reactivity maintenance. Therefore, there is a further need to develop sulfur-carbon composites having excellent stability and electrochemical reactivity.

[ Prior art documents ]

[ patent document ]

Korean patent application publication No. 2016-0046775 (2016, 4, 29), a negative electrode for a lithium sulfur battery and a method for preparing the same.

Korean patent application publication No. 2016-.

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

As a result of extensive studies in view of the above circumstances, the inventors of the present invention have confirmed that, by introducing a coating layer comprising a polymer having an electrolyte supporting ability on the surface of a porous carbon material, the accessibility and the contact of an electrolyte are improved to thereby improve the electrochemical reactivity of a sulfur-carbon composite material and the performance of a battery comprising the sulfur-carbon composite material.

Accordingly, an aspect of the present invention provides a sulfur-carbon composite material capable of maintaining initial capacity and life characteristics by forming a coating layer including a polymer having an electrolyte supporting ability between a porous carbon material and sulfur.

Another aspect of the present invention provides a positive electrode including the sulfur-carbon composite and a lithium sulfur battery including the positive electrode.

[ technical solution ] A

According to one aspect of the present invention, there is provided a sulfur-carbon composite material comprising a porous carbon material; a polymer having electrolyte supporting capability; and sulfur.

At least either one of the inner surface and the outer surface of the porous carbon material may comprise a coating layer containing the polymer having electrolyte supporting ability.

The sulfur-carbon composite material may be in a state in which the porous carbon material having the coating layer formed thereon is mixed with the sulfur.

The polymer may have an electrolyte loading capacity of 50% or more.

The polymer having electrolyte supporting capability may comprise a polymer selected from the group consisting of polyurethane, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyolefin, poly (meth) acrylate, polymethyl methacrylate, polycarbonate, polymethyl carbonate, polyethyl

At least one member selected from the group consisting of oxazoline, polyvinyl acetate, polyvinyl chloride, polyvinyl ether, and polyvinyl pyrrolidone.

The polymer having an electrolyte supporting ability may be included in an amount of 0.1 to 50 parts by weight, based on 100 parts by weight of the porous carbon material.

According to another aspect of the present invention, there is provided a positive electrode for a lithium sulfur battery, comprising the sulfur-carbon composite.

According to still another aspect of the present invention, there is provided a lithium sulfur battery including the positive electrode.

[ PROBLEMS ] the present invention

The sulfur-carbon composite according to the present invention is provided with a coating layer containing a polymer having an electrolyte-supporting ability on the surface of a porous carbon material, and is capable of improving reactivity with sulfur by maintaining an electrolyte uniformly inside the composite, whereby performance and life characteristics of a lithium-sulfur battery can be improved.

Drawings

Fig. 1 is a graph showing charge and discharge capacities of coin-type batteries according to experimental example 1 of the present invention.

Fig. 2 is a graph showing the discharge performance of the coin type battery according to experimental example 1 of the present invention.

Detailed Description

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as limited to common meanings or dictionary meanings, and should be construed as meanings and concepts conforming to the technical idea of the present disclosure on the basis of the principle that the inventor of the present application can appropriately define the concept of the terms to best describe the present invention.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms also include the plural forms unless the context clearly dictates otherwise. In the present invention, terms such as "including" or "having" are used to indicate the presence of the features, numerals, steps, actions, components, or combinations thereof described in the specification, and are required to be interpreted as not excluding the possibility of one or more other features, numerals, steps, actions, components, or combinations thereof being present or added.

The term "composite material" used in the present specification means a material that combines two or more materials and exhibits a more effective function while forming physically and chemically different phases.

The term "electrolyte supporting ability" used in the present specification refers to an ability to contain and hold an electrolyte, and is distinguished from temporary contact or uptake of a corresponding material or component in that the electrolyte is uniformly supported for a long time.

Lithium sulfur batteries have high discharge capacity and theoretical energy density in many lithium secondary batteries, and have been receiving attention as next-generation batteries, which are advantageous in that resources of sulfur used as a positive electrode active material are abundant and inexpensive, and are environmentally friendly.

However, sulfur is reduced from cyclic S in lithium sulfur batteries ₈ Conversion to linear lithium polysulphides (Li) ₂ S _x X ═ 8, 6, 4, and 2), and when such lithium polysulfide is completely reduced, lithium sulfide (Li) is finally produced (Li) ₂ S). Among such lithium polysulfides as an intermediate product of the reduction reaction of sulfur, lithium polysulfides having a high sulfur oxidation number (Li) ₂ S _x Usually x>4) Is a material having strong polarity, and thus is easily dissolved in an electrolyte solution containing a hydrophilic organic solvent to be eluted from the positive electrode reaction region and no longer participate in the electrochemical reaction. In addition, since sulfur becomes lithium sulfide (Li) as a discharge product ₂ S) to cause a volume expansion of about 80%, thereby reducing the void volume inside the positive electrode, resulting in a problem of difficulty in contact with the electrolyte. In addition to this, there occurs a problem that the electrolyte solution is decomposed and consumed due to the formation of a passivation layer (solid electrolyte interphase, SEI) or reaction with impurities when driving the battery.

Since the amount of sulfur participating in the electrochemical reaction is low with the loss of sulfur and electrolyte and the large change in the volume of the positive electrode, the lithium sulfur battery has problems in that theoretical capacity and energy density cannot be completely achieved in practical driving and the decrease in initial capacity and cycle characteristics is accelerated after a certain cycle, in spite of the above advantages.

In the prior art, methods of high loading of sulfur, improving the quality of mixing with a conductive material, introducing a coating layer that functions to suppress the elution of lithium polysulfide, and the like have been used, but these methods have not been effective in improving the performance of lithium sulfur batteries.

In view of the above, in order to improve reactivity between a sulfur-carbon composite material and an electrolyte and improve capacity and cycle characteristics of a lithium sulfur battery by providing a function capable of locking an electrolyte inside the sulfur-carbon composite material, i.e., between sulfur and a carbon material, the present invention provides a sulfur-carbon composite material comprising a carbon material having a coating layer formed of a polymer having an electrolyte supporting ability.

Specifically, the sulfur-carbon composite material according to the present invention comprises: a porous carbon material; a polymer having electrolyte supporting capability; and sulfur, wherein at least either one surface of the inner surface and the outer surface of the porous carbon material comprises a coating layer containing the polymer having an electrolyte supporting ability.

The porous carbon material of the present invention comprises a coating layer containing the polymer having an electrolyte supporting ability on at least either one of the inner surface and the outer surface. By stably holding the electrolyte impregnated with the polymer having electrolyte supporting ability inside the sulfur-carbon composite material, i.e., between sulfur and the carbon material, the accessibility of the electrolyte inside the active material can be improved and the electrochemical reactivity of sulfur can be increased. In particular, even when the electrolyte/sulfur (E/S) ratio is decreased, specifically to 3.5 or less, in order to improve the battery energy density, or the void volume inside the positive electrode is decreased due to the generation of lithium sulfide, the reaction with sulfur is continuously performed by the impregnated electrolyte existing between the porous carbon material and sulfur, and the initial capacity and cycle characteristics of the lithium-sulfur battery can be maintained for a long time.

In the present invention, the polymer may have an electrolyte loading capacity of 50% or more, preferably 200% or more and more preferably 200% to 600%. Here, the electrolyte loading capacity can be measured by preparing the corresponding polymer into a film and calculating the weight difference between before and after impregnation in the electrolyte. Specifically, the respective polymers are cast by dissolving in an appropriate solvent and then dried to prepare a polymer film, and as an example, the respective polymers may be applied in a proportion of 0.1 to 50 parts by weight with respect to 100 parts by weight of the porous carbon material. In addition, an electrolyte containing a lithium salt such as LiFSI or LiTFSI and an ether solvent is used. The prepared polymer film was immersed at 25 ℃ for 48 hours to allow the electrolyte to be impregnated into the coated polymer until saturation, and the weight at this time was taken as the weight after immersion.

The polymer having an electrolyte supporting ability is a material that does not react with a solvent used in preparing an electrolyte or a positive electrode slurry, and examples thereof may include materials selected from the group consisting of polyurethane, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyolefin, poly (meth) acrylate, polymethyl methacrylate, polycarbonate, polymethyl carbonate, polyethyl carbonate

At least one member selected from the group consisting of oxazoline, polyvinyl acetate, polyvinyl chloride, polyvinyl ether, and polyvinyl pyrrolidone. Preferably, the polymer having electrolyte supporting capability may be polyurethane.

Polyurethanes can be prepared by the reaction of polyols with isocyanates.

The polyol is generally used for preparing the polyurethane and is not particularly limited, and specific examples thereof may include at least one selected from the group consisting of polyether polyol, polyester polyol, polytetramethylene ether glycol polyol, polyurea dispersion (PHD) polyol, amine-modified polyol, and mannich polyol.

Further, the isocyanate reacted with the polyol is generally used for preparing the polyurethane and is not particularly limited, and specific examples thereof may include one selected from the group consisting of Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), 4 ' -dicyclohexylmethane diisocyanate (H12MDI), polyethylene polyphenyl isocyanate, Toluene Diisocyanate (TDI), 2 ' -diphenylmethane diisocyanate (2,2 ' -MDI), 2,4 ' -diphenylmethane diisocyanate (2,4 ' -MDI), 4 ' -diphenylmethane diisocyanate (4,4 ' -MDI, monomeric MDI), polymeric diphenylmethane diisocyanate (polymeric MDI), o-toluidine phenyl methane diisocyanate (TODI), Naphthalene Diisocyanate (NDI), Xylene Diisocyanate (XDI), Lysine Diisocyanate (LDI) and triphenylmethane triisocyanate (TPTI).

Weight average molecular weight (M) of polymer having electrolyte supporting ability _w ) There is no particular limitation, and those commonly used in the art may be used without limitation. As an example, the polymer having an electrolyte supporting capacity may have a weight average molecular weight of 5000g/mol to 4000000g/mol and preferably 100000g/mol to 1000000 g/mol.

The polymer having the electrolyte supporting ability may be used in an amount of 0.1 to 50 parts by weight and preferably in an amount of 1 to 25 parts by weight based on 100 parts by weight of the porous carbon material. When the content of the polymer having the electrolyte supporting ability is less than the above range, the formation of the coating layer on the porous carbon material is insufficient, and the target effect of improving the reactivity of the sulfur-carbon composite may not be obtained. On the other hand, the content greater than the above range may adversely affect the preparation process of the positive electrode slurry, the function as a positive electrode active material, and the battery performance.

The porous carbon material provides a skeleton capable of uniformly and stably fixing sulfur as a positive electrode active material, and supplements the conductivity of sulfur to smoothly perform an electrochemical reaction.

Porous carbon materials can generally be prepared by carbonizing precursors of various carbon materials. The porous carbon material includes irregular pores therein, and the pores have an average diameter in a range of 1nm to 200nm, and a pore density or porosity may be in a range of 10% to 90% of a total volume of the porous carbon material. When the pores have an average diameter smaller than the above range, the pore size is only at a molecular level, thereby making impregnation of sulfur impossible, and when the pores have an average diameter larger than the above range, the mechanical strength of the porous carbon is weakened, which is not preferable for use in the electrode preparation process.

The porous carbon material may be in the form of a sphere, a rod, a needle, a plate, a tube, or a block, and may be used without limitation as long as it is generally used in a lithium sulfur battery.

The porous carbon material may be used without limitation as long as it is a material having a porous structure or a high specific surface area and is generally used in the art. Examples of the porous carbon material may include a material selected from the group consisting of graphite; graphene; carbon blacks such as DENKA black, acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; carbon Nanotubes (CNTs), such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs); carbon fibers such as Graphite Nanofibers (GNF), Carbon Nanofibers (CNF), or Activated Carbon Fibers (ACF); at least one of the group consisting of natural graphite, artificial graphite, expanded graphite, and activated carbon, but is not limited thereto. The porous carbon material may preferably be carbon nanotubes.

The sulfur may comprise sulfur selected from inorganic sulfur (S) ₈ )；Li ₂ S _n (n is more than or equal to 1); disulfide compounds, such as 2, 5-dimercapto-1, 3, 4-thiadiazole or trithiocyanuric acid; an organic sulfur compound; and carbon-sulfur polymer ((C) ₂ S _x ) _n X is 2.5 to 50, n is 2) or more. Preferably, inorganic sulfur (S) may be used ₈ )。

In the sulfur-carbon composite material according to the present invention, the weight ratio of the porous carbon material including the above coating layer to sulfur may be 1:9 to 5:5 and preferably 2:8 to 3: 7. When the weight ratio is less than the above range, the addition amount of the binder required for preparing the cathode slurry may increase as the content of the porous carbon material increases. Such an increase in the amount of addition of the binder may thus increase the sheet resistance of the electrode, thereby functioning as an insulator that prevents electron transfer (passage of electrons), and the battery performance may thus be degraded. In contrast, when the weight ratio is greater than the above range, sulfur itself is aggregated, and since sulfur hardly accepts electrons, it may become difficult to directly participate in the electrode reaction.

In addition, in the present invention, the sulfur-carbon composite material may include 50 to 90: 6-45: 0.01-15 weight ratio of sulfur, porous carbon material and polymer with electrolyte loading capacity. When the composition ratio in the sulfur-carbon composite material corresponds to the above range, the effect of improving the electrochemical reactivity and stability of the above sulfur-carbon composite material can be secured.

Further, in the sulfur-carbon composite material according to the present invention, sulfur is located on at least either one of the inner surface and the outer surface of the pores of the porous carbon material, and thus may be present in a region of less than 100%, preferably 1% to 95%, and more preferably 60% to 90%, of the entire inner surface and outer surface of the porous carbon material. When sulfur is present on the surface of the porous carbon material within the above range, the greatest effect can be obtained in terms of the electron transfer area and the wettability of the liquid electrolyte. Specifically, sulfur is impregnated onto the surface of the porous carbon material in a thin and uniform manner in the region of the above range, and thus the electron transfer contact area during charge and discharge can be increased. When sulfur is located in 100% area of the entire surface of the porous carbon material, the porous carbon material is completely covered with sulfur, thereby decreasing the wettability of the electrolyte and reducing the contact with the conductive material contained in the electrode, and therefore electrons cannot be transferred and participation in the reaction becomes impossible.

The sulfur-carbon composite material of the present invention may further comprise a conductive material.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes of the battery. As examples of the conductive material, carbon blacks such as Super-P, DENKA carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; carbon derivatives such as carbon nanotubes or fullerenes; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; or a conductive polymer such as polyaniline, polythiophene, polyacetylene or polypyrrole.

In addition, the invention provides a preparation method of the sulfur-carbon composite material.

The method for preparing the sulfur-carbon composite material according to the present invention is not particularly limited, and methods generally known in the art may be used.

The preparation method of the sulfur-carbon composite material according to the present invention may comprise the steps of: (a) coating a porous carbon material with a polymer having electrolyte supporting ability; and (b) mixing the porous carbon material coated with the polymer having electrolyte supporting ability prepared in step (a) with sulfur, and molding the resultant.

The step of forming a coating layer with a polymer having an electrolyte supporting ability on the surface of the porous conductive material may be performed by the following procedure: the porous conductive material is introduced into a solution in which a polymer having an electrolyte supporting ability is dissolved, the resultant is stirred, and then filtered and dried, however, any method known in the art may be used.

Step (b) may be carried out by the following procedure: the porous carbon material coated with the polymer having the electrolyte supporting ability is mixed with sulfur and the resultant is heated and shaped, however, any method known in the art may be used.

The mixing serves to increase the degree of mixing between the above materials and may be performed using a stirring device commonly used in the art. Here, the mixing time and the mixing rate may also be selectively controlled according to the content of the raw materials and conditions.

The heating temperature may be any temperature as long as it is a temperature at which sulfur is melted, and specifically, may be 120 ℃ to 180 ℃ and preferably 150 ℃ to 180 ℃. When the heating temperature is less than 120 ℃, sulfur may not be sufficiently melted and a sulfur-carbon composite structure may not be properly formed, and when the temperature is more than 180 ℃, the coated polymer may not be retained, thereby making it difficult to obtain a target effect. In addition to this, the heating time may be controlled according to the sulfur content.

By the above production method, a sulfur-carbon composite material having a coating layer containing a polymer having an electrolyte supporting ability between a porous carbon material and sulfur can be produced, and by the sulfur-carbon composite material in which an electrolyte is supported via the coating layer formed between the porous carbon material and sulfur, the electrochemical reactivity of sulfur and the electrolyte is increased, which can improve the battery performance by maintaining the initial capacity and cycle life characteristics of the battery for a long time.

In addition, the present invention provides a positive electrode for a lithium sulfur battery, comprising the sulfur-carbon composite material.

The sulfur-carbon composite material may be included in a positive electrode as a positive electrode active material.

The positive electrode may further include one or more additives selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur, in addition to the positive electrode active material.

The transition metal element may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, Hg, and the like. As the group IIIA element, Al, Ga, In, Ti, etc. may be contained, and as the group IVA element, Ge, Sn, Pb, etc. may be contained.

The positive electrode may further include, together with the positive electrode active material or optionally with the additive, a conductive material for smooth migration of electrons in the positive electrode and a binder for good adhesion of the positive electrode active material to a current collector.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and as the conductive material, carbon blacks such as Super-P, Denka carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, or carbon black may be used alone or as a mixture; carbon derivatives such as carbon nanotubes or fullerenes; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; or a conductive polymer such as polyaniline, polythiophene, polyacetylene or polypyrrole.

The conductive material may be added in an amount of 0.01 to 30 wt% based on the total weight of the mixture including the cathode active material.

The binder has a function of holding the positive electrode active material on the positive electrode current collector and organically connecting the positive electrode active material, and examples thereof may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine-containing rubber, various copolymers thereof, and the like.

The binder may be included in an amount of 0.5 to 30 wt% based on the total weight of the mixture including the cathode active material. When the content of the binder is less than 0.5 wt%, the physical properties of the positive electrode are degraded, causing the active material and the conductive material in the positive electrode to fall off, and when the content is more than 30 wt%, the ratio of the active material and the conductive material in the positive electrode is relatively reduced, thereby decreasing the battery capacity.

When the method for producing the positive electrode of the present invention is specifically studied, the binder is first dissolved in the solvent used for producing the slurry, and then the conductive material is dispersed therein. As the solvent used for preparing the slurry, a solvent capable of uniformly dispersing the positive electrode active material, the binder, and the conductive material and easily evaporating is preferably used, and typical examples thereof may include acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropanol, and the like. Next, the conductive material is uniformly dispersed again in the solvent in which the conductive material is dispersed together with the positive electrode active material, or optionally together with an additive, to prepare a positive electrode slurry. The amount of the solvent, the positive electrode active material, or the additive optionally contained in the slurry is not significant in the present application, and it is sufficient that the slurry has an appropriate viscosity for easy coating.

The slurry prepared as described above was coated on a current collector, and the resultant was vacuum-dried to form a positive electrode. The slurry may be coated on the current collector to an appropriate thickness according to the viscosity of the slurry and the thickness of the positive electrode to be formed.

The current collector is generally not particularly restricted so long as it can be generally prepared to have a thickness of 3 to 500 μm, to have high conductivity, and not to cause chemical changes in the battery. Specifically, a conductive material such as stainless steel, aluminum, copper, or titanium may be used, and more specifically, an aluminum current collector coated with carbon may be used. The use of carbon coated aluminium substrates has the following advantages compared to the use of aluminium substrates without a carbon coating: the adhesive strength to the active material is excellent, the contact resistance is low, and corrosion of aluminum by polysulfide is prevented. In addition, the current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a nonwoven fabric.

Further, the present invention provides a lithium sulfur battery comprising: a positive electrode comprising the above sulfur-carbon composite material; a negative electrode; and an electrolyte interposed between the positive electrode and the negative electrode.

The positive electrode is a positive electrode according to the present invention and is the same as described above.

The anode may be formed of a current collector and an anode active material layer formed on one surface or both surfaces of the current collector. Alternatively, the negative electrode may be a lithium metal plate.

The current collector is used to support an anode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in a voltage region of a lithium secondary battery. Examples thereof may include copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc.

The anode current collector may enhance the binding strength with the anode active material by forming fine irregularities on the surface thereof, and various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, or a non-woven fabric may be used.

As the negative electrode active material, a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy may be used.

Examples of the material capable of reversibly intercalating or deintercalating lithium ions may include crystalline carbon, amorphous carbon, or a mixture thereof.

Examples of the material capable of reversibly forming a lithium-containing compound by reacting with lithium ions may include tin oxide, titanium nitrate, or silicon.

Examples of the lithium alloy may include an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

A separator may be additionally included between the positive electrode and the negative electrode. The separator separates or insulates the positive electrode and the negative electrode from each other and enables transfer of lithium ions between the positive electrode and the negative electrode, and may be formed of a porous non-conductive material or an insulating material. Such a separator may be a separate member such as a film, or a coating added to the positive electrode and/or the negative electrode.

Examples of the material forming the separator may include polyolefins such as polyethylene and polypropylene; the glass fiber filter paper and the ceramic material, but are not limited thereto, and the thickness may be about 5 μm to about 50 μm and preferably about 5 μm to about 25 μm.

The electrolyte is located between the positive electrode and the negative electrode, and includes a lithium salt and a nonaqueous organic solvent.

The concentration of the lithium salt may be 0.2M to 2M, specifically 0.6M to 2M and more specifically 0.7M to 1.7M, depending on various factors such as the precise composition of the electrolyte, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the operating temperature, and other factors known in the art of lithium batteries. When the lithium salt concentration less than 0.2M is used, the conductivity of the electrolyte may be reduced, resulting in a decrease in the performance of the electrolyte, and when the lithium salt concentration greater than 2M is used, the viscosity of the electrolyte is increased, resulting in a decrease in the mobility of lithium ions.

The lithium salt may be used without limitation as long as it is generally used for a liquid electrolyte for a lithium sulfur battery. Examples thereof may comprise a compound selected from the group consisting of LiSCN, LiBr, LiI, LiPF ₆ 、LiBF ₄ 、LiB ₁₀ Cl ₁₀ 、LiSO ₃ CF ₃ 、LiCl、LiClO ₄ 、LiSO ₃ CH ₃ 、LiB(Ph) ₄ 、LiC(SO ₂ CF ₃ ) ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiCF ₃ CO ₂ 、LiAsF ₆ 、LiSbF ₆ 、LiAlCl ₄ And LiFSI, lithium chloroborane, lithium lower aliphatic carboxylate, and the like.

As the nonaqueous organic solvent, a nonaqueous organic solvent generally used for an electrolyte solution for a lithium secondary battery can be used without limitation. For example, an ether, an ester, an amide, a chain carbonate, a cyclic carbonate, or the like may be used alone or as a mixture of two or more kinds as the organic solvent. Among these, ether compounds are generally included.

Examples of the ether compound may include at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxy ethane, diethoxy ethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, 1, 3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran, however, the ether is not limited thereto.

Examples of the ester as the organic solvent may include any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, γ -valerolactone, γ -caprolactone, σ -valerolactone and ∈ -caprolactone, or a mixture of two or more thereof, however, the ester is not limited thereto.

Specific examples of the chain carbonate may include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, Ethyl Methyl Carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, or a mixture of two or more thereof, however, the chain carbonate is not limited thereto.

Specific examples of the cyclic carbonate may include any one selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, vinylene carbonate, ethylene carbonate, and halides thereof, or a mixture of two or more thereof.

Examples of their halides may include fluoroethylene carbonate (FEC) and the like, but are not limited thereto.

In addition, in addition to the above organic solvents, N-methylpyrrolidone, dimethylsulfoxide, sulfolane, and the like can be used.

In addition to the above composition, the electrolyte may further contain a nitric or nitrous compound commonly used in the art. Examples thereof may include lithium nitrate (LiNO) ₃ ) Potassium nitrate (KNO) ₃ ) Cesium nitrate (CsNO) ₃ ) Magnesium nitrate (MgNO) ₃ ) Barium nitrate (BaNO) ₃ ) Lithium nitrite (LiNO) ₂ ) Potassium nitrite (KNO) ₂ ) Cesium nitrite (CsNO) ₂ ) And so on.

The electrolyte may be injected at an appropriate stage in the manufacturing process of the electrochemical device, depending on the manufacturing process and desired physical properties of the final product. In other words, the electrolyte may be used at a stage before the electrochemical device is assembled or at a final stage of the electrochemical device assembly.

The lithium sulfur battery according to the present invention may be subjected to lamination (stacking) and folding processes of a separator and an electrode, in addition to winding as a general process.

The shape of the lithium sulfur battery is not particularly limited, and various shapes such as a cylindrical shape, a laminate type, or a coin type may be used.

In addition, the present invention provides a battery module including the lithium sulfur battery as a unit cell.

The battery module may be used as a power source for medium to large-sized devices requiring high-temperature stability, long cycle characteristics, and high rate characteristics.

Examples of the medium to large-sized devices may include power tools driven by receiving power through a battery motor; electric vehicles including Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and the like; an electric two-wheeled vehicle including an electric bicycle (e-bike) and an electric scooter (e-scooter); an electric golf cart; a system for storing electricity, and the like, but is not limited thereto.

[ detailed description of the invention ]

Hereinafter, preferred embodiments will be provided to illustrate the present invention, however, the following embodiments are only for illustrative purposes, and it will be apparent to those skilled in the art that various changes and modifications may be made within the scope and technical concept of the present invention and also fall within the scope of the appended claims.

Examples and comparative examples

[ example 1]

Carbon nanotubes (1g) were introduced into a solution in which polyurethane (Elastollan1180A, a product of BASF Corporation) was dissolved at 1.5% in N-methyl-2-pyrrolidone, and the resultant was stirred at 80 ℃ for 12 hours, washed and dried to form a polyurethane coating on the surface of a porous carbon material. Here, the polyurethane to porous carbon material has a weight ratio of 2: 8. Here, the porous carbon material means the total weight of the carbon nanotube.

After the polyurethane-coated porous carbon material (1.25g) prepared above and sulfur (3g) were uniformly mixed, the resultant was heat-treated at 155 ℃ for 30 minutes to prepare a sulfur-carbon composite material comprising sulfur to the porous carbon material to polyurethane in a weight ratio of 66:27: 7.

After preparing a slurry using the sulfur-carbon composite prepared as described above in a weight ratio of sulfur-carbon composite to conductive material to binder of 92:3:5, the slurry was coated on an aluminum foil current collector having a thickness of 20 μm to prepare an electrode. Here, carbon black is used as the conductive material, and styrene-butadiene rubber and carboxymethyl cellulose are used as the binder.

Comparative example 1

An electrode was prepared in the same manner as in example 1, except that carbon nanotubes having no polyurethane coating layer formed were used.

Experimental example 1: evaluation of Charge and discharge Properties

Each of the electrodes prepared in examples and comparative examples was used as a positive electrodeA lithium sulfur battery coin cell was fabricated using polyethylene as the separator and a lithium foil having a thickness of 150 μm as the negative electrode. Here, the coin type cell was used by mixing 1M LiFSI and 1% LiNO ₃ An electrolyte prepared by dissolving diethylene glycol dimethyl ether and 1, 3-dioxolane (DEGDME: DOL ═ 6:4 (volume ratio)) in an organic solvent.

For the manufactured coin-type batteries, the capacity from 1.8V to 2.5V was measured using a charge and discharge measuring device (LAND CT-2001A, Wuhan blue Electronics co. Further, the discharge capacity and coulombic efficiency (CC: constant current, CV: constant voltage) were measured by continuously performing cycles of charging at 0.1C rate CC/CV and discharging at 0.1C, 0.2C, and 0.5C rate CC. The results obtained here are shown in table 1 below, fig. 1 and fig. 2.

[ TABLE 1]

From table 1, it was confirmed that the charge and discharge performance of the coin type battery including the positive electrode according to the present invention was superior as compared to the comparative example.

Specifically, it was confirmed that the capacity of the coin-type battery of example 1 was improved as compared to comparative example 1, as shown in table 1 and fig. 1.

Further, when table 1 and fig. 2 were studied, it was confirmed that although the coulombic efficiency of example 1 and the coulombic efficiency of comparative example 1 were similar, the discharge capacity of the coin-type battery including the positive electrode of example 1 was higher and the discharge capacity retention ratio was improved in the entire cycle as compared with comparative example 1. From the results, it was confirmed that the performance and life characteristics of the battery comprising the sulfur-carbon composite material of the present invention were superior.

Claims

1. A sulfur-carbon composite comprising:

a porous carbon material;

a polymer having electrolyte supporting capacity; and

the amount of sulfur is such that,

wherein the porous carbon material provides a framework to immobilize the sulfur,

wherein at least one of an inner surface and an outer surface of the porous carbon material comprises a coating layer containing the polymer having electrolyte supporting ability, the coating layer being formed between the porous carbon material and the sulfur,

wherein the polymer having electrolyte loading capability comprises a polymer selected from the group consisting of polyurethane, polypropylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyolefin, poly (meth) acrylate, polycarbonate, polyethyl

At least one of the group consisting of oxazoline, polyvinyl acetate, polyvinyl chloride, polyvinyl ether and polyvinylpyrrolidone,

wherein the polymer having an electrolyte supporting ability is contained in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the porous carbon material.

2. The sulfur-carbon composite material according to claim 1, wherein the sulfur-carbon composite material is in a state in which the porous carbon material having the coating layer formed thereon is mixed with the sulfur.

3. The sulfur-carbon composite of claim 1, wherein the polymer has an electrolyte loading capacity of 50% or more.

4. The sulfur-carbon composite material according to claim 1, wherein the porous carbon material contains at least one selected from the group consisting of graphene, carbon black, carbon nanotubes, carbon fibers, natural graphite, artificial graphite, expanded graphite, and activated carbon.

5. The sulfur-carbon composite of claim 1, wherein the sulfur comprises at least one selected from the group consisting of:

S ₈ ；

Li ₂ S _n wherein n is more than or equal to 1; and

an organic sulfur compound.

6. A method of making the sulfur-carbon composite of claim 1, comprising the steps of:

(a) coating a porous carbon material with a polymer having an electrolyte supporting ability; and

(b) mixing the porous carbon material coated with the polymer having electrolyte supporting ability prepared in step (a) with sulfur, and molding the resultant,

7. The method for producing the sulfur-carbon composite material according to claim 6, wherein the step (b) comprises mixing the porous carbon material coated with the polymer having electrolyte supporting ability with sulfur and heating and molding the resultant.

8. A positive electrode for a lithium-sulfur battery, comprising the sulfur-carbon composite material according to any one of claims 1 to 5.

9. A lithium sulfur battery comprising the positive electrode of claim 8.